1. Field of the Invention
The present invention generally relates to systems and methods for controlling the ignition coil charge time (dwell duration) of an internal combustion engine.
2. Description of the Known Technology
Internal combustion (IC) engines, such as those commonly found in automobiles, are designed to maximize power while meeting exhaust emission requirements with minimal fuel consumption. The combustion process of an IC engine can be controlled in a closed loop using in-cylinder ionization feedback. In this case, engine control computer routinely monitors the ionization current from each individual cylinder of the engine in order to determine combustion information. Depending on the ionization current, the engine control computer may make adjustments to maximize power, minimize fuel consumption and avoid undesirable engine operational conditions, such as engine knock and misfire.
In a conventional spark ignited internal combustion engine, the combustion is initiated by an ignition coil, which causes the electrical discharge (spark) of a spark plug. The duration of this ignition coil charge time is known as a dwell. Increasing the dwell increases the engine combustion stability due to increased spark energy and voltage. However, increasing the dwell duration increases electrical spark energy, leading to long spark duration. This long spark duration inhibits ionization current measurement, thereby preventing the engine control computer from receiving a proper ionization current signal. Illustrative of this problem is the spark occurring at high engine speeds, such as 6000 rpm. At such engine speeds, Spark duration of one millisecond can cover approximately 36 degrees of crank rotation. Accordingly, the ionization current cannot be detected during that period, resulting in a situation where no combustion information is provided to the engine control computer. Without this combustion information, the engine closed loop control computer cannot make the necessary adjustments to avoid engine knock and misfire. Therefore, there is a need for a system and method that controls the dwell duration to allow measurement of the ionization current at high engine speeds while maintaining engine combustion stability.